Understanding Tension Member Sections

In steel structures, tension members are structural elements designed to carry tensile loads, which are forces that pull on the member, tending to stretch it. The efficiency of a tension member section depends on how effectively the cross-sectional area is utilized to resist the load and how well the load is transferred into the member, especially at connections.

Analyzing Different Tension Member Sections

Let's look at the common sections used as tension members and their characteristics:

• Bolted single – angle section: When a single angle is connected by one leg, the load transfer is not uniform across the entire section. This leads to a phenomenon called shear lag, where the unconnected leg doesn't fully participate in carrying the load near the connection. This reduces the effective area and efficiency. Bolted connections can also reduce the effective area due to bolt holes.
• Welded single – angle section: Welding a single angle can provide a more uniform connection compared to bolting, potentially reducing shear lag compared to a single-leg bolted connection. However, shear lag can still be a significant factor, especially in longer connections.
• Channel section: Channel sections can be used as tension members. Their performance depends on how they are connected. Connecting through the web or flanges can influence load distribution and shear lag.
• Double – angle section on opposite side of gusset plate: This configuration involves two angle sections placed back-to-back but on opposite sides of a gusset plate. When connected to the gusset plate (typically through both legs of each angle or the outstanding legs), this arrangement offers significant advantages:
  • Improved Load Distribution: Placing angles on opposite sides of the gusset and connecting both legs (or equivalent) allows for a more balanced and uniform transfer of load into both angle sections.
  • Reduced Shear Lag: By connecting both legs, the effect of shear lag is significantly minimized compared to a single angle connected by only one leg. This ensures a larger portion of the cross-sectional area is effective in resisting the tensile force.
  • Increased Stiffness: This arrangement provides better stiffness and stability against buckling or vibrations, although buckling is less critical for pure tension members, stiffness is beneficial.
  This symmetrical or near-symmetrical connection helps in distributing stress more evenly across the combined section of the two angles.

Determining the Best Tension Member Section

Considering the effectiveness in load transfer and minimization of shear lag, the double – angle section connected on opposite sides of a gusset plate is generally considered the best option among the choices provided for a tension member. This configuration ensures that the maximum possible area of the section contributes to resisting the tensile load, leading to higher efficiency and strength compared to single angles or channel sections connected in ways that induce significant shear lag.